In gas turbine engines, the turbine discs for the high and intermediate pressure turbines are supported by bearings held within a common bearing hub. An example of such a bearing hub is an inner annular wall enclosing the bearing, and an outer annular wall surrounding the inner wall. The region between the inner and outer walls accommodates buffer sealing air to prevent leakage of oil out of the bearing chamber. It is important that the inner and outer walls are fixedly held together to provide sufficient rigidity for the respective turbines.
The outer wall is subjected to high temperatures, and this can cause considerable expansion. The inner wall is, on the other hand, subjected to much lower temperatures, and expands to a lesser degree. This differential thermal expansion of the inner and outer walls creates stress and can result in failure of the bearing hub.